What's the point behind 45 man game day rosters?

[El Duderino]

Teams carry 53 players on their rosters, but on game days are only allowed to have 45 of those players active to play in the game.

What is the reason behind this, it makes no sense to me? All 53 players will get a game check for that day, yet only 45 are allowed to play in the game, it seems silly to me. If a guy is on the 53 man roster and is getting paid a game check, why the hell shouldn't every one of those players be available to play in each given game?

[MickeyDavis]

It was a compromise in the CBA. Owners wanted smaller rosters, union wanted larger. But the 8 get paid less than if they were on the regular roster. They make $5200 per week or $88,400 for the 17 week season if they are on the PS that long. If they were on the regular roster they would make at least $285,000.

[El Duderino]

I'm not talking about the practice squad guys

I meant on game days that of the actual 53 man roster, not practice squad guys, only 45 players of that 53 can be active, the other 8 are in street clothes. From week to week the inactive guys often change depending on health reasons or if the team feels it might need say more or less WR's active given who they play.

[MickeyDavis]

Sorry I misread your original post. Yeah it makes no sense.